With the booming of the World Interoperability for Microwave Access (WiMax), the third generation mobile communication system has to improve its network performance and reduce costs of the network construction and operation to maintain its powerful competence in the mobile communication field. Therefore, the standardization workgroup of the 3rd Generation Partnership Project (3GPP) is currently focusing on the research of the evolution of the Packet Switch Core (PS Core) and the Universal Mobile Telecommunication System Radio Access Network (UTRAN) as the research project is called System Architecture Evolution (SAE) aiming at higher transmission rate, shorter transmission time delay, optimized packet, and support of mobility management among the Evolved UTRAN (E-UTRAN), UTRAN, Wireless Local Area Network (WLAN) and other non-3GPP access networks provided by the Evolved Packet Core (EPC).
The current architecture of the SAE is as shown in FIG. 1, and contains the following network elements:
an Evolved RAN (E-RAN): an Evolved Radio Access Network, providing higher uplink/downlink rate, lower transmission delay and more reliable wireless transmission. The network element included in the E-RAN is an Evolved NodeB (eNodeB) for providing the user access with wireless resources;
a Packet Data Network (PDN): a network for providing users with services;
an E-Packet Core: an evolved packet network for providing lower delay and allowing accesses of more radio access systems. It contains the following network elements:
a Mobility Management Entity (MME), a control plane function entity, a server for storing user data temporarily, being responsible for managing and storing the context of a User Equipment (UE) (e.g. identification of the UE/user, mobility management status, and user security parameter etc), allocating temporary identifications to users, when the UE is located in the tracking area or the network, performing authentication to the user, processing all non-access-stratum messages between the MME and the UE, and triggering the paging in the SAE. The MME is a mobility management unit of the SAE system. In the UMTS system, the mobility management unit is a Serving General Packet Radio Service (GPRS) Support Node (SGSN);
a Serving Gateway (S-GW): this gateway is a user plane entity, being responsible for processing the user plane data routing, and terminating the downlink data of the UE in an idle (ECM_IDLE) state, managing and storing the SAE bearer context of the UE, such as IP bearer service parameter and network interior routing information etc. The S-GW is an anchor point of the interior user plane in the 3GPP system and there is only one S-GW for one user at one time;
a Packet Data Network (PDN) gateway (P-GW): a gateway being responsible for enable the UE to access the PDN, allocating IP address for users, and meanwhile being the mobility anchor point of the access systems of the 3GPP and the non-3GPP. The functions of the PDN GW further include: policy implementation, charging support. A user may access multiple PDN GWs simultaneously. A Policy and Charging Enforcement Function (PCEF) entity is also located in the PDN GW;
a Policy and Charging Rules Function (PCRF) entity is responsible for providing the PCEF with policy control and charging rules.
a Home Subscriber Server (HSS) for permanently storing user subscription data. The contents stored in the HSS include an International Mobile Subscriber Identification (IMSI) of the UE and the IP address of the PDN GW;
Physically, the S-GW and the PDN GW may be combined as one. The user plane network elements of the EPC system include the S-GW and the PDN GW.
A Radio Network Controller (RNC) connects to the SGSN via an Iu interface, the SGSN connects to the MME via an S3 interface, connects to the S-GW via an S4 interface, and connects to the HSS via a Gr interface; the HSS connects to the MME via an Sha interface, the MME connects to the eNodeB via an S1-MME interface, and connects to the S-GW via an S11 interface; the S-GW connects to the eNodeB via an S1-U interface, and connects to the P-GW via an S5 interface; the P-GW connects to the PDN via an SGi interface, and connects to the PCRF entity via an S7 interface, the PCRF entity connects to the PDN via a Rx+ interface.
When the coverage area in which the UE resides is changed, for example, on moving from a Radio Access Technology (RAT) coverage area to another RAT coverage area, the UE finds entering a unregistered area by monitoring a broadcast channel; it is necessary for the UE to register in the new RAT coverage area to guarantee the serving continuous between the UE and the core network; therefore, the UE may initiate a Tracking Area Update (TAU) procedure or a Routing Area Update (RAU) procedure of an inter RAT. FIG. 2 is a TAU procedure caused by the UE registered in the UTRAN coverage area moving to the E-UTRAN coverage area. The RAU procedure caused by the UE registered in the E-UTRAN coverage area moving to the UTRAN coverage area is similar to that of FIG. 2, which is not described again. As shown in FIG. 2, the procedure includes the following steps:
step 201, the UE moves to the E-UTRAN coverage area of the MME, sends to the MME a tracking area updating request for registering in the new area; the request message carries a P-TMSI allocated to the UE by the SGSN;
step 202, the new MME finds an old SGSN according to the P-TMSI identification, and sends a context request signaling to perform a context acquiring process;
step 203, the old SGSN sends the mobility management and bearer information of the user to the new MME, i.e. performing the context response;
step 204, after receiving the corresponding information, the new MME confirms the context, i.e. context confirmation;
step 205, the new MME initiates to the S-GW an updating bearer request carrying a source GTP-C tunnel identification and a destination GTP-C tunnel identification; the S-GW updates the binding relationship of the bearer;
step 206, the S-GW sends to the P-GW the updating bearer request which sends parameters of the address information of the S-GW, the tunnel identification information and the accessing technology type to the P-GW;
step 207, the P-GW updates its context and returns to the S-GW an updating bearer response information carrying the address of the P-GW and the tunnel identity etc;
step 208, the S-GW returns to the new MME an updating bearer response which sends the destination GTP-C tunnel identification designated by the S-GW, the address of the S-GW, the address of the P-GW and the tunnel information to the MME;
step 209, the new MME notifies the HSS of changing the registered location via a location updating message;
step 210, the HSS keeps the single registering principle for the UE, sends a location cancel signaling to the old SGSN, and only maintains the registration of the new MME;
step 211, the old SGSN returns a location cancel response to the HSS;
step 212, the HSS confirms the location update of the new MME;
step 213, if confirming that the UE is valid within the current tracking area, the new MME sends a tracking area updating accept message to the UE;
step 214, if the new MME allocates a new GUTI identification to the UE via a TAU procedure, the UE returns a tracking area updating completion message to the MME for confirming.
Based on such a location update principle, if the UE moves frequently between the UTRAN coverage areas or the E-UTRAN coverage areas, or the frequent registering area selection caused by the signal strength and etc within the same coverage area may trigger plenty of the TAU or the RAU procedures, which causes heavy burden to air interfaces. Therefore, in an EPS system, an Idle mode Signaling Reduction (ISR) function is introduced to reduce the air interface signaling between the UE and the core network. When the function is activated, the UE having both the UTRAN and E-UTRAN accessing function may register to the MME and the SGSN at the same time. Therefore, on moving frequently between two different accessing technologies, the UE does not initiate the TAU or the RAU of the inter RAT, so as to reduce the unnecessary air interface signaling transmission.
The procedure of the ISR activating by the UE is also implemented through the TAU or the RAU procedure, however, there are differences of some steps. The differences between the above two procedures are hereinafter described in detail by taking that the ISR function is activated by using the TAU procedure of FIG. 3 for example. As shown in FIG. 3, the procedure includes the following steps:
step 301, the UE moves to the E-UTRAN coverage area of the MME, sends to the MME the tracking area updating request carrying the capability of whether the UE supports the ISR apart from the P-TMSI allocated to the UE under the SGSN;
step 302, the new MME finds the old SGSN according to the P-TMSI identification, and sends the context request signaling to perform the context acquiring process;
step 303, the old SGSN sends the mobility management and bearer information of the user to the new MME, and carries the capability of whether the old SGSN supports the ISR in the returned context response message;
step 304, the new MME determines whether to activate the ISR according to the context information received from the old SGSN; if it is necessary for activating the ISR, the new MME returns to the old SGSN the context confirmation message which carries an ISR indication for notifying the old SGSN of keeping the original context information of the UE;
step 305, the new MME initiates to the S-GW the updating bearer request carrying the source GTP-C tunnel identification and the destination GTP-C tunnel identification; the S-GW updates the binding relationship of the bearer. The updating bearer request message further includes the activating ISR indication for notifying the S-GW of keeping the bearer context information of the UE under the old SGSN.
step 306, since the RAT is changed, the S-GW sends the updating bearer request to the P-GW;
step 307, the P-GW updates its context and returns the updating bearer response message to the S-GW;
step 308, the S-GW returns to the new MME the updating bearer response carrying the destination GTP-C tunnel identification designated by the S-GW, the address of the S-GW, the address of the P-GW and the tunnel information etc;
step 309, the new MME notifies the HSS of location change via the location updating message, and notifies the HSS of the ISR activating information via a corresponding identification, then the HSS keeps the dual registration information of the E-UTRAN domain and the UTRAN domain, does not send the location cancel information to the old SGSN;
For the above corresponding identification information, the dual registration is currently indicated by the existing information element of location updating type.
step 310, it is determined whether the UE activates the ISR; if the HSS does not keep the dual registration of the UE, it sends the location cancel signaling to the SGSN; if the ISR is activated, the HSS keeps two PS domain registration of the UE, it does not send the location cancel signaling to the old SGSN, which belongs to the second case in the procedure;
step 311, if the SGSN receives the location cancel signaling, it returns a location cancel response to the HSS; corresponding to step 310, it is not necessary to return the location cancel response in the procedure;
step 312, the HSS confirms the location update of the new MME;
step 313, if confirming that the UE is valid within the current tracking area, the new MME sends the tracking area updating accept message to the UE; the MME notifies the UE that the ISR function is activated by an indication in the message;
step 314, if the new MME allocates a new GUTI identification to the UE via the TAU procedure, the UE returns the tracking area updating completion message to the MME for confirming.
When the ISR is activated, the S-GW keeps the bearer information of two access networks at the same time, it is necessary to distinguish the control plane information from the MME or from the SGSN, so as to guarantee that the bearer accessing network is operated correctly. The control plane information between the MME and the SGSN is transmitted via the GTP-C tunnel; the source terminal and the destination terminal of the tunnel are identified by using the TEID.
As can be seen from the above description, the S-GW is notified to activate the ISR function via the updating bearer request of step 305 at present, and the message indicates the S-GW to bind the new bearer information and the original bearer information to the GTP-C tunnel identification of the same destination. In this way, the S-GW is unable to distinguish the subsequent control plane signaling from which mobility management unit; therefore, the corresponding bearer can not be updated or released.